The beneficial effects of physical exercise on physical, emotional and social development of children have been widely publicised,¹ as well as its important role in preventing chronic diseases in adults. In contrast, physical inactivity is an independent risk factor for cardiovascular diseases.^{2 – 6}

Although the cardiovascular benefits of regular physical exercise are well established, participation in physical activities imposes a risk of sudden cardiac death, with a 2.8-fold increase in risk compared to sedentary individuals.⁷ Sudden death, despite being a rare event, is highly relevant in public health, as it affects presumably healthy young people, and may be the first manifestation of heart disease and arrhythmia.^{8 , 9}

In Italy in 1982, an evaluation program was implemented for 12 to 35-year-old athletes before participating in physical activities; this included electrocardiogram (ECG), medical history and clinical examination; after 15 years, a 90% reduction in the incidence of sudden death was observed.⁷ In 2004, the International Olympic Committee and, in 2005, the European Society of Cardiology established protocols recommending the inclusion of ECG in routine evaluation of athletes,^{7 , 10} in contrast to the American Heart Association (AHA), that does not recommend including ECG in the evaluation of all athletes prior to sports activities. The AHA recommends a medical history focusing on personal and family history of heart disease in addition to clinical examination,^{10 – 13} which is followed by the American Academy of Pediatrics.¹⁴

In 2013, the Brazilian Society of Cardiology and the Brazilian Society of Sports Medicine 1st Guideline on Sports and Exercise Cardiology was published, recommending ECG for children and adolescents before physical activities, which was confirmed in 2019.^{15 , 16}

Considering this divergence in orientation between the main cardiology societies in the world, our study aims to identify cardiac changes detected only by ECG in the evaluation of children and adolescents before the practice of physical activities.

We recruited asymptomatic children and adolescents between five and 17 years old who wanted to practice regular physical activities, mainly soccer or futsal. Convenience sampling was used from social projects in the city . Invitees were included in the study when parents or legal guardians (and those over 10 years old) agreed to participate and signed the free and informed consent form, in accordance with the norms of the National Commission of Ethics in Research (CONEP).

The assessment consisted of four stages: identification; anthropometry; clinical examination with attention to cardiovascular status; and ECG. Before the evaluation, medical history was taken with the parents or guardians to exclude patients with any known heart disease or electrocardiographic alterations.

Anthropometric measurements, clinical examination and ECG were performed during participants’ social project activities. Weight and height were measured with participants wearing light clothes and no shoes, and then body mass index (BMI) and its respective BMI-for sex/age Z score (World Health Organization – WHO) were calculated using AnthroPlus software.^{17 , 18}

Clinical examination was focused on cardiovascular health status. Blood pressure (BP) was measured in the right arm after a period of rest, with individuals seated and cuff size appropriate to the arm circumference. BP was considered increased when systolic or diastolic BP measurements were above the 90th percentile for height, age and gender.^{19 , 20}

Standard 12-lead ECG was performed at rest, with individuals in the supine position, by a pediatric cardiologist using a Tecnologia Eletrônica Brasileira (TEB) device and the ECGPC software. All ECG were recorded on the researcher's personal computer and backed up.

This study included a convenience sample of 983 children and adolescents, of which 835 (84.9%) were male. Participant distribution by age and gender is shown in Table 1 . Median age for males was 10.8 years (IQR, interquartile range 8.3 -13.6 years). Female median age was 11.2 years (IQR 9.3 - 13.0 years).

Concerning nutritional status ( Table 2 ), a higher frequency (not statistically significant) of overweight, obesity and severe obesity was observed in females than males, and a statistically higher frequency of normal weight in males than females.

Analysis of BMI Z-score distribution showed some differences compared to the WHO normality curve ( Graph 1 ). We noticed that individuals in this study were generally shorter and heavier compared to WHO standard values.

Clinical changes are shown in Table 3 . The most frequent was heart murmurs, in 182 cases (81.7% of the clinical findings and 18.5% in all the study sample). Elevated BP was observed in 26 (2.6%) participants, corresponding to 11.7% of the clinical changes. Heart murmur and pectus excavatum were more common in males, and high BP in females, with a statistically significant difference for pectus excavatum only (p < 0.05).

Electrocardiographic changes were detected ( Table 4 ) in 32 (3.3%) children and adolescents. The main alterations were ventricular extrasystoles in seven (0.7%) participants, and intraventricular conduction disturbances, also in seven (0.7%). No statistical difference between genders was seen.

Of the 983 children and adolescents evaluated, 223 (22.6%) had clinical abnormalities ( Table 3 ) and 32 (3.2%) electrocardiographic abnormalities ( Table 4 ). Of these 13 participants showed both clinical and electrocardiographic abnormalities concomitantly.

Nineteen participants had electrocardiographic changes only, that is, had no personal or family history of heart disease and no clinical changes. In this subgroup, the following changes were found – ventricular extrasystoles; intraventricular conduction disorders; ectopic atrial rhythm; left ventricular overload; left anterior hemiblock; preexcitation syndrome (Wolff-Parkinson-White); first-degree atrioventricular block; sinus bradycardia and paroxysmal supraventricular tachycardia. This reinforces the importance of ECG in the evaluation of children and adolescents before beginning physical activities.

In this study, distribution of participants by BMI z-score was different compared to the WHO curve. In females, there was a high prevalence of overweight and obesity, and these conditions are known to be associated with comorbidities^{23 – 25} like arterial hypertension, insulin resistance, dyslipidemia, non-alcoholic fatty liver disease and metabolic syndrome. Although pharmacological treatment is possible, the main therapy is lifestyle change, with nutritional monitoring and regular physical activity.^{23 , 25}

Although a few variables showed statistically significant differences between genders (prevalence of normal weight and pectus excavatum), our study has a selection bias due to the greater number of male participants, most of whom practiced soccer or futsal as their main sport. Sampling was by convenience, with children and adolescents recruited from social projects, which may justify our findings.

While some medical societies such as the American Heart Association and the American Academy of Pediatrics do not recommend performing routine ECG in asymptomatic patients with no personal or family history of cardiovascular disease before physical activities.^{10 – 13} Our results showed electrocardiographic abnormalities in asymptomatic children and adolescents that may lead to unfavourable outcomes. Although the frequency of these abnormalities was low, these children and adolescents may be at increased risk to develop heart diseases, and also sudden death from cardiac cause (e.g. Wolff-Parkinson-White syndrome and paroxysmal supraventricular tachycardia.^{26 – 28} Our results support the recommendations of the European Society of Cardiology, the Brazilian Society of Cardiology and the Brazilian Society of Sports Medicine, that for the pediatric population undergo ECG before engaging in physical activities.^{7 , 10 , 15 , 16}

We identified electrocardiographic changes not only in patients with cardiovascular abnormalities, but also in those with normal cardiovascular status at clinical examination. We can therefore say that a normal cardiovascular examination does not exclude the need for an ECG in evaluating children and adolescents who practice regular physical activities. Another important aspect is that both physical examination and ECG are performed with the patient at rest, but many heart diseases only generate symptoms during physical exertion; in other words, the number of alterations may be even greater if the patient was assessed during physical exertion or an exercise test.²⁹ Massin showed that the stress test can show specific alterations, mainly hemodynamic ones and, in terms of prognosis of heart disease, it plays an important role in evaluating these children.²⁹

It is important to point out that some changes found in children and adolescents are physiological, such as an innocent heart murmur. However, differentiating between a physiological and a pathological change may be difficult, thus reinforcing the need for electrocardiographic evaluation. Even the American Heart Association recommends performing an ECG in patients with presumed physiological alterations.¹⁰

Parents or guardians of participants who presented clinical or electrocardiographic changes were informed about them and referred to the Pediatric Cardiology outpatient clinic of a public or private service, according to parental choice, for diagnostic investigation.

This study has some limitations. We studied a convenience with a predominance of males, as participants were recruited from social projects in which the main sports activities were soccer and futsal. In addition, some individuals already practiced regular physical activities, and we cannot rule out the possibility that the electrocardiographic changes found at rest may be in fact related to these activities. However, our objective was to detect electrocardiographic abnormalities that might be associated with an increased risk of sudden death and undetected by medical history or physical examination.

In addition to medical history and clinical examination, ECG should be part of the evaluation of children and adolescents before starting regular physical activities.